People walk past a banner for Hosei University near the entrance to the university's Tama campus after a woman brandished a hammer inside a classroom, in Machida in the western suburbs of Tokyo on Jan 10, 2025. (Photo: AFP: Philip Fong)
A 22-year-old student who identified herself as South Korean was arrested on the spot Friday on suspicion of assault, a Tokyo police spokesman told AFP.
Several reports had said people were seen bleeding from the head after the attack, which public broadcaster NHK said had been motivated by frustration over bullying, citing investigative sources.
The attacker began swinging a hammer in the classroom "all of a sudden", a student who witnessed the incident told Japanese broadcaster TV Asahi.
"Everyone was panicking. I was so scared at first that my hands were shaking."
The eight who were hurt all received medical treatment and ended up requiring no hospitalisation, Hosei University said in a statement late Friday.
"We will cooperate with police investigations and care for students and faculty shocked by the incident," the institution said, adding efforts would be made to "ensure campus safety".
Violent crimes are rare in Japan due in part to strict gun control.
But there are occasional stabbings and even shootings, including the assassination of former prime minister Shinzo Abe with a homemade gun in 2022.
In December, a junior high school student was stabbed to death and another was wounded at a McDonald's restaurant in southwestern Japan. A man was later arrested over the attack.
In January 2022, three people were stabbed outside the prestigious University of Tokyo before nationwide college entrance exams.